This invention relates to microfibers of a extrudable polymers and nonwoven mats prepared therefrom.
The present invention also relates to a melt-blowing process for the production of the microfibers and the nonwoven mats.
Microfibers and nonwoven mats thereof invention are used in many fields where fibers have been used, particularly in the fields of filtration and insulation. The microfibers of the prior art as well as nonwoven mats or webs thereof are produced by a variety of various melt-blowing processes which have been described heretofore in patents and literature.
U.S. Pat. No. 2,411,660 describes a melt-blowing process for the manufacture of nonwoven fabrics from plastics for abrading, scouring, filtering, etc. U.S. Pat. No. 3,849,241 discloses a process for producing a melt-blown nonwoven mat wherein a fiber-forming thermoplastic polymer resin having a specific initial intrinsic viscosity is subjected to degradation in the presence of a free radical source compound. Several melt-blowing processes for the production of a nonwoven thermoplastic fabric or a composite thereof are taught in U.S. Pat. Nos. 4,041,203; 4,100,324; 4,196,245; 4,302,495; 4,379,192; and 4,767,825. R. L. Shambaugh discussed several factors of a melt-blowing process using dimensional analysis in "A Macroscopic View of the Melt-Blowing Process for Producing Microfibers", Ind. Eng. Chem. Res., Vol. 27, No. 12, 2363-72 (1988).
The aforementioned patents indicate that a broad range of plastic materials may be used for producing nonwoven mats of microfibers. U.S. Pat. No. 2,411,660 states that a great variety of plastics may be used, such as vinylidene chloride, polystyrene, polyphenylenesulphide, polyvinyl alcohol, polyvinyl acetate, methyl methacrylate, polymeric amide, copolymer of vinyl chloride and vinyl acetate, latex compositions, cellulosic and petroleum derivatives, protein-base materials, glass, etc. U.S. Pat. Nos. 4,041,203 and 4,100,324 describe that among the many useful thermoplastic polymers, polyolefins such as polypropylene and polyethylene, polyamides, polyesters such as polyethylene terephthalate, and thermoplastic elastomers such as polyurethanes are anticipated to find the most wide spread use in the preparation of the materials described herein (nonwoven thermoplastic fabrics of miorofibers). U.S. Pat. No. 4,379,192 discloses that linear polyethylene, polyisobutylene, polybutadiene, polyurethanes, polyvinyls, polyamides and polyesters, can be used as starting material for microfibers in addition to isotactic polypropylene which is considered as a most preferred material.
U.S. Pat. No. 4,767,825 discloses superabsorbent thermoplastic compositions and melt-blown or spun bonded webs prepared therefrom. The thermoplastic composition comprises from 86 to 98 percent by weight of a poly(oxyethylene)diol soft segment and from 2 to 14 percent by weight of a hard segment which is selected from polyurethanes, polyamides, polyesters, polyureas and mixtures thereof. Unfortunately, these polymers are often either difficult to melt-blow or spin into microfibers or do not have the chemical resistance, toughness and dimensional stability required for many applications.
Therefore, it is desirable to provide a microfiber and a nonwoven mat, fabric, web, or similar structure prepared from a polymer which is easily melt-blown or spun into microfibers exhibiting good chemical resistance excellent toughness and good dimensional stability.